A novel polarization-reconfigurable planar antenna is presented. The antenna consists of an electronically reconfigurable polarizer integrated with a printed slot. By changing the states of the p-i-n diodes on the polarizer, the linearly polarized (LP) waves radiated by the slot can be converted into either right-hand circularly polarized (RHCP) or left-hand CP (LHCP) waves. The polarizer contains 16 unit cells arranged as a 4 × 4 array. The antenna radiates RHCP waves if the p-i-n diodes on the top side of the polarizer are switched ON, while LHCP waves are radiated if the p-i-n diodes of the bottom side of the polarizer are switched ON instead. The physical mechanisms of the antenna are discussed and the parametric study is carried out by full-wave simulations. To verify the concept, one prototype at 2.5 GHz is designed, fabricated, and measured. Good agreement between the measured and simulated results is obtained. The antenna achieves a gain ≥8.5 dBic in both RHCP and LHCP with an aperture efficiency of 70%. Advantages of the proposed design include electronically reconfigurable polarizations for RHCP or LHCP, low profile, low cost, high isolation between the dc bias circuit and RF signals, high power handling capability, and easy extension to large-scale arrays without increasing the complexity of the dc bias circuit. To the best of our knowledge, this is the first report of an electronically polarization-reconfigurable CP antenna with a single-substrate polarizer.

This article proposes a convenient technique for determining the permittivity and permeability of materials placed in a waveguide. Simplicity and repeatability of the method are achieved due to the utilization of contactless waveguide flanges and short-short-line (SSL) calibration technique. The grooves in the contactless flange prevent the electromagnetic field from leaking through the gap between the flanges even though misalignments exist. The SSL calibration uses a single line standard and two short standards. Since only one line standard is required, the test fixtures do not need to move during the calibration and measurement. With the help of contactless flanges and SSL calibration technique, the test fixtures could stay fixed in a plastic bracket. In addition, the line standard, the short standards, and the device under test (DUT) can be easily replaced without fastening screws. It is convenient when there are a large number of samples to be measured. The measured permittivity and permeability of polytetrafluoroethylene (PTFE) and carbonyl iron powders in the whole X-band showed the validity of the contactless flange and the accuracy of the SSL calibration technique.

A type of ultrawideband (UWB) absorber, comprising a tightly coupled array (TCA) in the UHF band, is proposed and designed in this communication. The absorber is based on the TCA concept and antenna reciprocity. Therefore, it inherits the UWB and ultrathin properties from TCAs. The proposed absorber consists of an air layer, a patterned indium-tin-oxide (ITO) film, and two layers of superstrate from an FR4 slab and a Teflon slab. The patterned ITO film is a resistive sheet to dissipate the received electromagnetic energy. The proposed absorber does not require the feed network, which is complicated for bipolarized and balanced TCA antennas. The fabricated absorber presents an absorption rate over 90% within a fractional absorption bandwidth of 135% from 0.23 to 1.183 GHz, and it has a thickness of $0.117\lambda $ at the lowest frequency. Moreover, the proposed absorber is polarization insensitive and angularly stable. The simulation and measurement results show that the TCA concept works well in design of ultrathin UWB absorbers.

A frequency reconfigurable patch antenna using reed switches to connect the patch with the ground plane is proposed. Compared with other voltage-controlled switches like MEMS and PIN diodes, reed switches are controlled by a magnetic field which can penetrate the ground plane easily. In this way, the control circuit can be placed beneath the ground plane to avoid its impacts on the radiation performance of the antenna. Twenty-four reed switches are used to increase the reconfigurability of the antenna and to show the feasibility of our concept when multiple control circuits are used simultaneously. The presented antenna can be reconfigured to operate in the frequency range from 0.3 to 3 GHz, covering for a large number of communication services. Three operating modes of the antenna (with resonance frequencies at 0.8, 2, and 2.85 GHz, respectively) are presented to illustrate the feasibility of this method. The measured matching and radiation characteristics of the fabricated antenna prototype agree well with the simulations.

Resonant methods are well known for their accuracy in determining the complex permittivity of materials. However, to guarantee the accuracy, interference modes must be suppressed in the measurement band. In this paper, a multi-mode split rectangular cavity is designed and fabricated to measure low-loss anisotropic dielectric materials in the frequency range from 300 to 1000 MHz. Details of the cavity design are presented. Simulation results for a uniaxially anisotropic material validate both the setup and the processing. Moreover, validation measurements on a sheet of polytetrafluoroethylene (PTFE) are in agreement with the literature data, which indicate that the proposed method in this paper is reliable and accurate for low-loss complex permittivity characterization at hundreds of megahertz.

The focus of this letter is on a thin, lightweight, and highly effective microwave shielding composite material reinforced by long continuous fibers, which can be easily fabricated with 3-D printing technique. Numerous long continuous carbon fibers are put into a bundle, then many bundles are parallelly arranged in a periodic way, and then embedded into the matrix material to form a single layer. Multiple layers are stacked up one over the other to produce the laminated composite with fiber bundles in each layer orientated into different directions. Numerical investigations have been carried out to discuss various factors which influence the shielding effectiveness, and highly effective shielding is achieved by the two-cross-layer composite. It is easily fabricated via 3-D printing technique, and experimental results are obtained based on square waveguide device to demonstrate the numerical results.